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Summary of Significant Accounting Policies - Income Taxes (Detail) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Income Taxes [Line Items] |  |
Total amount of unrecognized tax benefits relating to uncertain tax positions | $ 35.4 |
Amount of unrecognized tax benefits change from year end relating to uncertain tax positions | (0.8) |
Decrease resulting from prior period tax positions | 2.9 |
Increase in unrecognized tax benefits resulting from expiration of statute of limitations periods | 2.1 |
Tax Act, one-time net tax benefits |  | $ (70.1)
Tax Act, benefits associated with re-measurement of deferred tax assets and liabilities |  | (85.3)
Tax Act, transition tax expense on post-1986 earnings and profits of certain foreign subsidiaries |  | 15.2
Tax Act, benefit associated with entity restructuring and recapitalization |  | (26.7)
Tax Act, expense associated with acceleration of certain deductions |  | $ 8.5
Maximum |  |
Income Taxes [Line Items] |  |
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months | $ 13.7 |

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- Definition Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) + References No definition available. + Details
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- Definition Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Entity Restructuring And Recapitalization, Provisional Income Tax Benefit + References No definition available. + Details
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- Definition Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d)(3) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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